Chapter 3: Genetics – Some Basic  Essential Fundamentals & Key Concepts | Class 10 Biology Answer set 🚀🔬

Chapter 3: Genetics – Some Basic  Essential Fundamentals & Key Concepts | Class 10 Biology Question set 🚀🔬

Chapter 3: Genetics – Some Basic  Essential Fundamentals & Key Concepts | Class 10 Biology Answer set 🚀🔬

ICSE CLASS 10 Genetics SirBikramSutradhar Bikram Sutradhar GrandMaster Bikram Sutradhar

✅ Check 1: Answer Set

Question 1: True or False

(i) ❌ False – Genetics and heredity are related but not identical. Genetics is the study of genes, while heredity refers to the passing of traits from parents to offspring.
(ii) ❌ False – The phrase “Like begets like” applies to both plants and animals, as offspring inherit characteristics from their parents.
(iii) ✅ True – All humans exhibit variations due to genetic recombination and environmental influences.

Question 2: Genetic Traits in Humans

Inherited Traits (✔) and Non-inherited Traits (❌):
(i) ❌ Ability to become a skilled cricketer (Skill is developed, not inherited)
(ii) ✔ Presence of curly hair (Inherited from parents)
(iii) ✔ Left-handedness (Genetically influenced trait)
(iv) ✔ Quality of voice (Partially inherited, but also affected by environment)
(v) ✔ Red-green color blindness (X-linked inherited disorder)

✅ Check 2: Answer Set

Question 1: Chromosome Count

(i) Humans have 23 pairs (46 total) of chromosomes 🧬.
(ii) There are 22 pairs of autosomal chromosomes (non-sex chromosomes).

Question 2: Only Daughters – Explanation

🔹 No, this does not indicate that the husband lacks Y-bearing sperm ❌.
🔹 The sex of a child is determined by the father’s sperm, which carries either an X (for a girl) or a Y (for a boy).
🔹 The fact that the couple has only daughters is due to chance and does not imply the absence of Y sperm.

✅ Check 3: Answer Set

Question 1: Unit of Heredity

🧬 Gene is the fundamental unit of heredity.

Question 2: Definitions

(i) Allele – Alternate form of a gene (e.g., tall (T) or dwarf (t) in pea plants).
(ii) Dominant Gene – A gene that expresses itself even if only one copy is present (e.g., “T” in “Tt”).
(iii) Genotype – The genetic makeup of an organism (e.g., TT, Tt, tt).
(iv) Phenotype – The physical expression of a trait (e.g., tall or short height).
(v) Recessive Gene – A gene that expresses itself only when both copies are recessive (e.g., “tt” for dwarf plants).

Question 3: Homologous Chromosome Count

(i) Human female – 23 homologous pairs (XX).
(ii) Human male – 22 homologous pairs + 1 non-homologous sex chromosome pair (XY).

Question 4: Heterozygous Recessive?

❌ No, a heterozygous recessive genotype is not possible.
🔹 “Heterozygous” means different alleles (Tt), while “recessive” requires both alleles to be the same (tt).

Question 5: Observable Traits in Humans

(i) Widow’s peak (Hairline shape)
(ii) Earlobe attachment (Attached or free)
(iii) Tongue rolling ability
(iv) Hitchhiker’s thumb (Bent or straight)

✅ Check 4: Answer Set

Question 1: Genetics Discovery

🧑‍🔬 Gregor Mendel is the “Father of Genetics” for his pioneering work on inheritance.

Question 2: Mendel’s Study Organism

📌 Common Name – Pea plant 🌱
📌 Scientific Name – Pisum sativum

Question 3: Differences

(i) Monohybrid vs. Dihybrid Cross – A monohybrid cross involves one trait (e.g., height), while a dihybrid cross involves two traits (e.g., height and color).
(ii) Genotype vs. Phenotype – Genotype is the genetic makeup (TT, Tt, tt), while phenotype is the observable characteristic (tall or short).
(iii) Character vs. Trait – Character is a general feature (e.g., flower color), while trait is a specific variation (e.g., purple or white flower).
(iv) Dominant vs. Recessive Allele – Dominant alleles express even in a single copy (T), while recessive alleles require two copies to be expressed (tt).
(v) Autosomes vs. Sex Chromosomes – Autosomes are non-sex chromosomes (22 pairs in humans), while sex chromosomes determine gender (XX for female, XY for male).

Question 4: Pea Pod Characteristics

🔹 Trait: Pod Color – Green (Dominant) vs. Yellow (Recessive)
🔹 Trait: Pod Shape – Inflated (Dominant) vs. Constricted (Recessive)

✅ Multiple-Choice Questions – Answer Key

1. (a) 3:1 ✅
2. (a) All tall ✅
3. (c) Independent assortment ✅
4. (c) Gs and gs ✅
5. (a) A recessive X-linked disorder ✅
6. (c) Phenotype ✅
7. (c) Law of segregation ✅
8. (d) 9:3:3:1 ✅
9. (c) Either X or Y chromosome ✅
10. (c) Carriers ✅

✅ Short & Descriptive Answers

1. Corrected Statements:
   (a) Centromere connects duplicated chromosomes.
   (b) The complete set of DNA in an organism is termed genome.
   (c) A characteristic that can be passed from one generation to another is known as a genetic trait.
   (d) Axial flower position is dominant in pea plants.
   (e)Try.
2. Why do lions, tigers, and domestic cats have 38 chromosomes but appear different?
   🔹 Despite having the same chromosome count, genetic variations and mutations lead to distinct species differences.
3. Garden Pea Plant Traits
   🔹 Flower color – Purple (Dominant) vs. White (Recessive)
   🔹 Seed shape – Round (Dominant) vs. Wrinkled (Recessive)
4. 🔹 Males (XY) have only one X chromosome, so if it carries the color-blindness gene, they express the trait. Females (XX) require two affected X chromosomes, which is rarer.

✅ Structured/Application-Based Answers

1. Bb x Bb (Black fur dominant over brown fur):
   🔹 Genotypic Ratio: 1 BB : 2 Bb : 1 bb
   🔹 Phenotypic Ratio: 3 Black : 1 Brown
2. Is coat color sex-linked?
   🔹 No, coat color is inherited independently of sex chromosomes.
3. Punnett Square Crosses:
   (a) TT x tt (Tall x Dwarf): 100% Tall (Tt)
   (b) RR x rr (Red x White Flowers): 100% Pink (Rr) in incomplete dominance.

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